diff -r 885ed790ecf0 -r c436414a719e src/cpu/x86/vm/assembler_x86_64.cpp
--- a/src/cpu/x86/vm/assembler_x86_64.cpp	Wed May 21 10:45:07 2008 -0700
+++ b/src/cpu/x86/vm/assembler_x86_64.cpp	Wed May 21 13:46:23 2008 -0700
@@ -683,7 +683,8 @@
 
   case REP8(0xB8): // movl/q r, #32/#64(oop?)
     if (which == end_pc_operand)  return ip + (is_64bit ? 8 : 4);
-    assert((which == call32_operand || which == imm64_operand) && is_64bit, "");
+    assert((which == call32_operand || which == imm64_operand) && is_64bit ||
+           which == narrow_oop_operand && !is_64bit, "");
     return ip;
 
   case 0x69: // imul r, a, #32
@@ -909,7 +910,8 @@
   } else if (r->is_call() || format == call32_operand) {
     opnd = locate_operand(inst, call32_operand);
   } else if (r->is_data()) {
-    assert(format == imm64_operand || format == disp32_operand, "format ok");
+    assert(format == imm64_operand || format == disp32_operand ||
+           format == narrow_oop_operand, "format ok");
     opnd = locate_operand(inst, (WhichOperand) format);
   } else {
     assert(format == 0, "cannot specify a format");
@@ -5157,12 +5159,9 @@
 void MacroAssembler::store_klass(Register dst, Register src) {
   if (UseCompressedOops) {
     encode_heap_oop_not_null(src);
-    // zero the entire klass field first as the gap needs to be zeroed too.
-    movptr(Address(dst, oopDesc::klass_offset_in_bytes()), NULL_WORD);
-    movl(Address(dst, oopDesc::klass_offset_in_bytes()), src);
-  } else {
-    movq(Address(dst, oopDesc::klass_offset_in_bytes()), src);
+    // Store to the wide klass field to zero the gap.
   }
+  movq(Address(dst, oopDesc::klass_offset_in_bytes()), src);
 }
 
 void MacroAssembler::load_heap_oop(Register dst, Address src) {
@@ -5188,13 +5187,15 @@
 void MacroAssembler::encode_heap_oop(Register r) {
   assert (UseCompressedOops, "should be compressed");
 #ifdef ASSERT
-  Label ok;
-  pushq(rscratch1); // cmpptr trashes rscratch1
-  cmpptr(r12_heapbase, ExternalAddress((address)Universe::heap_base_addr()));
-  jcc(Assembler::equal, ok);
-  stop("MacroAssembler::encode_heap_oop: heap base corrupted?");
-  bind(ok);
-  popq(rscratch1);
+  if (CheckCompressedOops) {
+    Label ok;
+    pushq(rscratch1); // cmpptr trashes rscratch1
+    cmpptr(r12_heapbase, ExternalAddress((address)Universe::heap_base_addr()));
+    jcc(Assembler::equal, ok);
+    stop("MacroAssembler::encode_heap_oop: heap base corrupted?");
+    bind(ok);
+    popq(rscratch1);
+  }
 #endif
   verify_oop(r, "broken oop in encode_heap_oop");
   testq(r, r);
@@ -5206,11 +5207,13 @@
 void MacroAssembler::encode_heap_oop_not_null(Register r) {
   assert (UseCompressedOops, "should be compressed");
 #ifdef ASSERT
-  Label ok;
-  testq(r, r);
-  jcc(Assembler::notEqual, ok);
-  stop("null oop passed to encode_heap_oop_not_null");
-  bind(ok);
+  if (CheckCompressedOops) {
+    Label ok;
+    testq(r, r);
+    jcc(Assembler::notEqual, ok);
+    stop("null oop passed to encode_heap_oop_not_null");
+    bind(ok);
+  }
 #endif
   verify_oop(r, "broken oop in encode_heap_oop_not_null");
   subq(r, r12_heapbase);
@@ -5220,11 +5223,13 @@
 void MacroAssembler::encode_heap_oop_not_null(Register dst, Register src) {
   assert (UseCompressedOops, "should be compressed");
 #ifdef ASSERT
-  Label ok;
-  testq(src, src);
-  jcc(Assembler::notEqual, ok);
-  stop("null oop passed to encode_heap_oop_not_null2");
-  bind(ok);
+  if (CheckCompressedOops) {
+    Label ok;
+    testq(src, src);
+    jcc(Assembler::notEqual, ok);
+    stop("null oop passed to encode_heap_oop_not_null2");
+    bind(ok);
+  }
 #endif
   verify_oop(src, "broken oop in encode_heap_oop_not_null2");
   if (dst != src) {
@@ -5237,14 +5242,16 @@
 void  MacroAssembler::decode_heap_oop(Register r) {
   assert (UseCompressedOops, "should be compressed");
 #ifdef ASSERT
-  Label ok;
-  pushq(rscratch1);
-  cmpptr(r12_heapbase,
-         ExternalAddress((address)Universe::heap_base_addr()));
-  jcc(Assembler::equal, ok);
-  stop("MacroAssembler::decode_heap_oop: heap base corrupted?");
-  bind(ok);
-  popq(rscratch1);
+  if (CheckCompressedOops) {
+    Label ok;
+    pushq(rscratch1);
+    cmpptr(r12_heapbase,
+           ExternalAddress((address)Universe::heap_base_addr()));
+    jcc(Assembler::equal, ok);
+    stop("MacroAssembler::decode_heap_oop: heap base corrupted?");
+    bind(ok);
+    popq(rscratch1);
+  }
 #endif
 
   Label done;
@@ -5277,6 +5284,19 @@
   leaq(dst, Address(r12_heapbase, src, Address::times_8, 0));
 }
 
+void  MacroAssembler::set_narrow_oop(Register dst, jobject obj) {
+  assert(oop_recorder() != NULL, "this assembler needs an OopRecorder");
+  int oop_index = oop_recorder()->find_index(obj);
+  RelocationHolder rspec = oop_Relocation::spec(oop_index);
+
+  // movl dst,obj
+  InstructionMark im(this);
+  int encode = prefix_and_encode(dst->encoding());
+  emit_byte(0xB8 | encode);
+  emit_data(oop_index, rspec, narrow_oop_operand);
+}
+
+
 Assembler::Condition MacroAssembler::negate_condition(Assembler::Condition cond) {
   switch (cond) {
     // Note some conditions are synonyms for others